Ultraviolet Photoemission and Inverse-Photoemission Spectroscopies of Diluted Magnetic Semiconductor Cd_ Mn_xTe

Valence-band and conduction-band densities of states (DOS's) of Cd1-xMnxTe epitaxial films (0 ≤ x ≤ 0.7) have been investigated by means of in situ measurements of ultraviolet photoemission and inverse-photoemission spectroscopies (UPS and IPES).\n\nBased on one-electron band theory, features observed at -3.4 and 3.6 eV relative to the valence-band maximum (VBM) are ascribed to emission from the Mn 3d↑ and 3d↓ states with eg symmetry, respectively, providing a Mn 3d spin-exchange splitting energy (Ueff) of 7.0±0.2 eV. This value compares well with the value predicted in the theoretical investigation of electronic structures and magnetic properties of Cd1-xMnxTe. With increasing Mn concentration, the energy position of the conduction-band minimum shifts almost linearly toward higher energy relative to the VBM as a result of an increasing contribution of the higher-lying Mn 4s level relative to the Cd 5s level.\n\nMn 3d partial DOS's in the valence-band region of Cd1-xMnxTe have been determined from resonant photoemission spectroscopy in the Mn 3p-3d core excitation region. The partial DOS's reveal an appreciable contribution of the Mn 3d states to the top 9 eV of valence bands with three structures; valence bands at 0~-2.5 eV, a main peak at -3.4 eV and a multielectron satellite at -5~-9 eV. These features are almost independent of the Mn concentration. Apart from one-electron band theory, the whole spectrum including the multielectron satellite is found to be well reproduced in terms of the configuration interaction theory using a Mn2+(Te2-)4 model cluster.\n\nElectronic structures of zinc-blende MnTe epitaxial films have also been investigated by means of UPS and IPES. The Ueff-value of zinc-blende MnTe is in good agreement with those of Cd1-xMnxTe and Zn 1-xMnxTe. The width of valence bands and Ueff are by 1.3 eV narrower and by 0.3 eV larger than those of NiAs-type MnTe, respectively.